Blood samples will be collected prior to initiation of therapy for DNA banking and DNA analysis (for all patients), for DNA analysis (TBI/VP16, Bu/Flu/Thiotepa and Treo/Flu/Thiotepa groups) and PK analysis (only for the Bu group). PK and pharmacogenomic data will then be correlated with the studied outcomes (e.g.Veno-occlusive disease, Graft vs host disease, Treatment Related Mortality, Events Free Survival, Overall Survival).